This invention relates to diagnosis and/or measurement of the optical properties of the eye. Embodiments of the present invention provide systems, devices, and methods to measure, diagnose and treat optical properties of an eye. Although specific mention is made to wavefront measurements of the eye, embodiments of the present invention can be used with many instruments that measure and/or treat optical properties of the eye, for example auto refractors and laser eye surgery systems.
The eye has many transparent tissue structures that are shaped to form images on the retina. Many of these tissue structures, such as the cornea and crystalline lens each contribute to the optical properties of the eye. Accurate measurements of these tissue structures and the overall refractive properties of the eye can be very helpful in the diagnosis and/or correction of optical defects of the eye. In some instances, the optical characteristics of the eye may change and can make accurate measurements of the eye difficult. For example, as patients age cataracts may form in the crystalline lens of the eye, and the cataracts may scatter light from a measurement device so as to degrade measurements of the eye.
The human eye is trained maintain focus on an object that it sees, even when the distance from the object to the eye changes. To maintain focus on an object, the crystalline lens of the eye may move and/or change shape so as to maintain focus. This ability of the eye to adjust and focus on a visual stimulus can be referred to as accommodation. Although the exact mechanism of accommodation has been debated in the scientific literature, one widely held view is that the eye may be considered in a relaxed state while viewing a distant object and muscles of the eye can contract to accommodate in response to a near object.
The accommodative state of the eye can effect the measured refractive properties of the eye. As accommodation changes the focus of the eye, a patient who has good distance vision with no refractive error can become myopic, or nearsighted, when the eye of the patient accommodates and focuses on a near object. In some instances, for example with instrument myopia, the patient may look into an instrument that is close to the patient and the eye may accommodate and adjust to near focus so as to become myopic while looking into the instrument, even though the fixation target of the instrument is positioned far from the patient.
With measurements of refractive properties of the eye, it can be desirable to make these measurements while accommodation the eye is relaxed and adjusted for distance vision. With correction of refractive error of the eye, it is often desirable to correct the patient's vision such that the patient will have good distance vision while accommodation of the eye is relaxed. This correction allows the patient to have good distance vision and use his or her accommodation to focus on near objects.
If a patient's eye accommodates for near vision during measurements of the eye's refraction, the patient may receive an improper amount of optical correction that can make the treatment less than ideal. For example with nearsightedness, overcorrection of the patient can result from patient accommodation for a near target during the refractive measurement of the eye. This overcorrection can make the patient far sighted, or hyperopic, once the accommodation relaxes. Consequently, the patient may not have good near vision as the patient may be unable to overcome the overcorrection to see objects that are near.
With the diagnosis and treatment of hyperopia, hyperopic patients often accommodate during both near and far vision so as to compensate for their hyperopia, such that these patients may have trouble relaxing their accommodation during measurements, even when viewing targets at a distance. Consequently, residual amounts of hyperopia may not be detected. Incomplete assessment of hyperopia can result in under correction and incomplete treatment of the patient's hyperopia, and the patient may need subsequent treatment as the patient ages and loses the ability to accommodate.
Many techniques can be used to decrease accommodation of the eye. For example, cycloplegic drops can be placed in the eye to paralyze an accommodative response of the eye. While effective, cycloplegic drops may often have side effects that can be undesirable for the patient. For example, the patient may not be able to read with distance correction, and pupil dilation resulting from such drops can make some patients sensitive to bright lights.
Another approach to minimize and relax accommodation during measurement of the eye is to provide a target at a distances that are progressively farther from the patient. This technique can be referred to as fogging the patient, in that the perceived target becomes blurry to the patient and the patient will tend to relax any accommodation to bring the more distant fogged target into focus. While fogging can be effective for many patients, some patients may not respond well to this technique.
Some measurement systems use light beams that may be at least partially visible to the patient and potentially interfere with the measurements of the eye. In some patients and measurement systems, visible measurement beams that are perceived by the patient may provide a visual stimulus in addition to the fixation target and interfere with the measurement of the patient. Although infrared light beams may be used that are invisible to the patient, the eye may refract and scatter infrared light differently than visible light, such that measurement errors can occur.
In light of the above, it would be desirable to have improved methods, devices, and systems for diagnosis and/or treatment of refractive error, aberrations, and other vision defects of the eye. It would also be desirable to have improved methods, devices, and systems for measuring the optical and/or visual response of the human viewing system and for developing new prescriptions to treat refractive error, aberrations, and other viewing defects. It would generally be desirable to increase the percentage of the population which can be effectively treated for refractive error, aberrations and other vision defects without greatly increasing the cost, risk, and/or complexity of diagnosis and/or treatment over current techniques. It would also be beneficial to have improved measurement devices and systems which enhanced the speed, ease of use, accuracy, and efficiency of obtaining wavefront measurements of a patient's eye, ideally while lowering the overall costs of such measurements.